My current bike has a 73mm BB shell width and I use a UN-91 (XTR) square taper BB that is 73x113mm. Is there anyway to use this in a bike frame that has a 68mm shell? My old bike mechanic brain is saying "no", but I was wondering if someone makes a spacer to make it work.
Yes... those old UN BB's had a press fit driveside cup that could be removed. You could then get drive and non-drive 68mm cups and it would work. The trick is, finding 68mm cups but some bike shops may have a good back stock of them if you ask around.
Why don't you just try going to your LBS to see if they have any 2.5mm BB spacers laying around? Most 73mm BBs come with these spacers so that you can mount this longer BB onto a shorter, 68mm, shell. If they have a customer who needs a replacement BB and their frame already has a 73mm shell then they just throw the extra spacers away. BTW, you only need one spacer for the drive-side.
Why don't you just try going to your LBS to see if they have any 2.5mm BB spacers laying around? Most 73mm BBs come with these spacers so that you can mount this longer BB onto a shorter, 68mm, shell. If they have a customer who needs a replacement BB and their frame already has a 73mm shell then they just throw the extra spacers away. BTW, you only need one spacer for the drive-side.
For that to work with this type of BB, the spacer would have to be between the interior of the cup, and the cartridge itself, and would force the cup 2.5mm closer to the crankarm, possibly causing them to bottom out on eachother (think classic XTR). mtnbiker72's plan ought to work; most established bike shops save those cups for later use and could cough up a set if you have the right type of beer :thumbsup:
For that to work with this type of BB, the spacer would have to be between the interior of the cup, and the cartridge itself, and would force the cup 2.5mm closer to the crankarm, possibly causing them to bottom out on eachother (think classic XTR). mtnbiker72's plan ought to work; most established bike shops save those cups for later use and could cough up a set if you have the right type of beer :thumbsup:
Now I'm completely confused. The OP is trying to put a 73mm BB onto a bike with a 68mm shell or am I wrong here? In order to do that you need a spacer between the drive-side cup and the BB shell, right? Or am I delusional?
ok, I am trying to visualize this - if you took my BB and screwed it in a 68 shelled frame, the spindle would not be centered about the frame, it would be longer on the non-drive side. So, the spacer between the drive side cup and the frame would center it correct?
Put one 2.5 mm spacer on the drive side like PCC posted and you'll be golden. The non-drive side will stick out a little, but what the hay.
Not sure what mechBgon was trying to say. The drive side cup is pressed on, it isn't going anywhere. Put a 2.5 mm spacer on that side, run it in, install the ND side cup and torque them down.
Wrong, the drive side cup is removable...I removed many on UN-91, UN-71, and UN-72 to switch from a 68mm to a 73mm and visa versa. They are not that hard to remove.
That said, a spacer on the driveside cup and a 68mm cup on the non-driveside would be a pretty clean install as well
Now I'm completely confused. The OP is trying to put a 73mm BB onto a bike with a 68mm shell or am I wrong here? In order to do that you need a spacer between the drive-side cup and the BB shell, right? Or am I delusional?
Mmm, coffee! Too bad the closest Peet's is so far away...
Glad to hear that I'm not delusional. I need to cancel my psychiatrist's apointment now
This is an older thread, you may not receive a response, and could be reviving an old thread. Please consider creating a new thread.
Related Threads
?
?
?
?
?
Mountain Bike Reviews Forum
15.4M posts
515.2K members
Since 1990
A forum community dedicated to Mountain Bike owners and enthusiasts. Come join the discussion about bike parts, components, deals, performance, modifications, classifieds, trails, troubleshooting, maintenance, and more!